Fluorine-containing polymers have been known for decades to be useful as protective coatings for various articles. For example, polytetrafluoroethylene (PTFE) has been widely used as a non-stick coating for kitchen utensils, such as frying pans, and tools, such as saws. PTFE and similar fluorine-containing polymers have also found use as hydrophobic protective layers for protecting surfaces against moisture.
More recently, Teflon® (PTFE) and perfluoroethylenepropylene have been used to coat the inner surfaces of aluminium canisters intended for use in the storage and administration of pulmonary medicaments (see EP 0 642 992). Khaladar, Mat Performance 1994, Vol. 33 part 2, 35–9, discloses fluoropolymer coatings for use as linings, whilst International patent application WO 96/32150 discloses fluoropolymer coatings for use as linings in the storage and administration of medicaments. The above coatings are intended to allow alternative propellant systems to be used, whilst preventing the contamination of medicaments with, for example, aluminium.
In the process and products described in EP 0 642 992, there is still a requirement that the process used to apply the coatings is improved, to reduce the roughness of the coatings. The preferred polymer blends of fluoropolymer and adhesive as disclosed in W/O 96/32150 are solvent based systems rather than aqueous systems. Hence, it is also desirable to reduce the quantity of extractable organic compounds used in coating processes (such as solvents) which may contaminate the contents of the container. The use of organic solvents that are flammable has a further drawback in that the equipment used for coating needs to be flame proofed. Also, these coatings require the addition of an adhesive to the polymer, otherwise the coating does not adhere sufficiently to the surface. Such adhesives may be costly and time consuming to apply, and may also be a source of drug contamination.
Accordingly, it is an object of the present invention to solve the problems associated with the prior art. It is also an object of the present invention to provide an improved process for coating an internal surface of a medicine storage container with a fluorine-containing polymer, to provide a finer, more even and unblemished coating with improved protective properties that requires no adhesive or primer, and which contains a minimum of extractable organic compounds. It is also an object of the present invention to provide a process for coating containers using an aqueous polymer suspension and to overcome the difficulties associated with producing good coatings from an aqueous suspension without using organic solvents.